Field of the Invention
The present invention relates to a copper foil, a copper-clad laminate board, a method for producing a printed wiring board, a method for producing an electronic apparatus, a method for producing a transmission channel, and a method for producing an antenna.
Related Art
Printed wiring boards have been largely developed over the recent half century, and now result in use in almost all electronic apparatuses. Following the recent increase of the demand of miniaturization and performance enhancement of electronic apparatuses, the enhancement of the mounting density of components and the increase of the signal frequency proceed, and the printed wiring boards are demanded to have an excellent capability under high frequency signals.
A high frequency substrate is demanded to have a reduced transmission loss for ensuring the quality of the output signal. The transmission loss is constituted mainly by a dielectric loss caused by a resin (i.e., a substrate) and a conductor loss caused by a conductor (i.e., a copper foil). The dielectric loss is decreased when the dielectric constant and the dielectric dissipation factor of the resin are decreased. The conductor loss in a high frequency signal is caused mainly in such a mechanism that the skin effect, in which an electric current having a higher frequency flows only a surface of a conductor, decreases the cross sectional area, through which an electric current flows, and thereby the resistance is increased. Accordingly, a high frequency circuit is necessarily formed with higher accuracy than the ordinary circuits, and excellent circuit formability is demanded.
As a technique for decreasing the transmission loss of the high frequency copper foil, for example, Patent Literature 1 describes a metal foil for a high frequency circuit containing a metal foil having coated on one surface or both surfaces thereof silver or a silver alloy, and having on the silver or silver alloy layer a coated layer formed in a thickness smaller than the silver or silver alloy layer. The literature describes that the metal foil can be provided that is reduced in loss due to the skin effect even in an ultrahigh frequency region used in satellite communications.
Patent Literature 2 describes a roughened rolled copper foil for a high frequency circuit, in which the integrated intensity (I(200)) of the (200) plane of the rolled surface of the rolled copper foil after recrystallization annealing obtained by X-ray diffraction is I(200)/I0(200)>40 with respect to the integrated intensity I0(200) of the (200) plane of fine powder copper obtained by X-ray diffraction, the arithmetic average roughness Ra of the roughened surface after performing a roughening treatment on the rolled surface by electrolytic plating is from 0.02 μm to 0.2 μm, the ten-point average roughness Rz is from 0.1 μm to 1.5 μm, and the copper foil is a material for a printed circuit board. The literature describes that a printed circuit board can be provided that is capable of being used under a high frequency exceeding 1 GHz.
Patent Literature 3 describes an electrolytic copper foil having on a part of the surface of the copper foil an uneven surface having a surface roughness of from 2 to 4 μm formed of bumpy protrusions. The literature describes that an electrolytic copper foil can be provided that is excellent in high frequency wave transmission characteristics.
Patent Literature 1: Japanese Patent No. 4,161,304
Patent Literature 2: Japanese Patent No. 4,704,025
Patent Literature 3: JP-A-2004-244656
As described in the foregoing, the conductor loss with a high frequency signal is mainly caused in such a mechanism that the cross sectional area of the conductor, through which an electric current flows, is decreased due to the skin effect, in which an electric current having a higher frequency flows only a surface of a conductor, and thereby the resistance is increased. A high frequency board that is capable of being folded in use for enhancing the degree of freedom in design is liable to cause cracks in the circuit, and the transmission loss is increased due to the influence of the cracks. The present inventors have found that the transmission loss of the high frequency circuit board can be favorably suppressed by suppressing cracks from being formed in a copper foil that is folded in use or bent in use.